Non-targeted tourism affects the behavioural budgets of bottlenose dolphins Tursiops truncatus in the South Adriatic (Montenegro)

Abstract

We investigated the short-term effects of non-targeted tourism on the behaviour of bottlenose dolphins Tursiops truncatus in the South Adriatic off the coast of Montenegro, by comparing dolphin group behaviour during impact (the presence of non-targeted tourism vessels) and control (absence of all marine vessels) scenarios. Tourism vessel and dolphin behavioural data were collected through systematic weekly land-based surveys. Using instantaneous focal ‘group’ scan sampling, the predominant behaviour of bottlenose dolphin groups was determined. To quantify the effect of vessel interactions on the behavioural budget of the dolphins, we followed a stepwise modelling approach. A first-order Markov chain was used to calculate the transition probabilities between behavioural states before a Monte Carlo simulation estimated the behavioural budgets of dolphins during impact and control situations. In the presence of non-targeted tourism, dolphins were found to be less likely to remain diving (during which dolphins were assumed to be feeding), whilst milling-socialising and surface feeding were completely absent from their behavioural repertoires. Nevertheless, the behavioural budgets demonstrated an increase in resting behaviour in the presence of non-targeted tourism vessels. No significant changes to travelling behaviour were observed. The decrease in foraging behaviour (both surface feeding and diving) could result in a reduction in energy intake for dolphins, which over time (assuming repeated disturbance) could negatively affect body condition, and ultimately survival and reproduction. Regulations on non-targeted tourism should therefore be considered to minimise potential long-term negative effects on dolphins within Montenegrin territorial waters.

Nautical tourism affects common bottlenose dolphin (Tursiops truncatus M.) foraging success in a NATURA 2000 site, North-Eastern Adriatic Sea

“…Following interactions with NTBs, dolphins increased their milling behaviour, with a significant decrease in their foraging behaviour. Although research throughout the Adriatic Sea has previously indicated that foraging behaviours are increased during spring and summer (Bearzi et al, 1999;Bearzi et al, 2008b;Affinito et al, 2018;Clarkson et al, 2020) and milling behaviours are least observed during the same seasons (Affinitio et al, 2018;Clarkson et al, 2020), the current study demonstrates a significant increase in milling behaviour upon interaction with NTBs which cannot be attributed to seasonality.…”

“…Significant decreases in foraging behaviour (which include diving and surface feeding behaviours) in bottlenose dolphins have also been reported elsewhere in the Adriatic Sea, despite much lower association rates with NTBs (Clarkson et al, 2020). It is well established that reductions in foraging behaviour reduce the energy intake of dolphins (Williams et al, 2006;Christiansen et al, 2010) and can lead to detrimental implications on the chances of survival and reproductive success if repeated disruptions occur (Lusseau, 2003;Constantine et al, 2004;Lusseau et al, 2006).…”

“…Regardless, concerns about the effects of dolphin and whale watching activities were raised and studies began to provide evidence of the significant effects that such activities had on cetacean behaviour (Lusseau & Higham, 2004;Stensland & Berggren, 2007;Christiansen et al, 2010;Steckenreuter et al, 2011;Christiansen et al, 2013a; Meissner et al, 2015). Despite this, few studies have documented the potential effects resulting from the interactions between cetaceans and NTB's within the Adriatic Sea (Rako et al, 2013;Clarkson et al, 2020).…”

“…High levels of boat traffic associated with nautical tourism have since become of particular concern in this region (Ribarič, 2013; and there is growing evidence that changes to cetacean behaviour are a response to increased nautical tourism activities (Lusseau, 2003;Christiansen et al, 2010;Pirotta et al, 2015;Clarkson et al, 2020). Short-term behavioural changes can include changes in vocalisation, changes in movement to avoid vessels (most often observed as increased dive durations, increased swimming speeds and/or increased frequency in changes of the travel direction) (Marley et al, 2017) and changes to behavioural activity (changes in the percentage of the time spent feeding, resting, or socialising) (Christiansen et al, 2010;Meissner et al, 2015;Clarkson et al, 2020). Changes in behavioural activity are most likely to incur energetic costs to animals which experience cumulative disturbances from non-targeted boat traffic (Clarkson et al, 2020) or are targeted by tourism (Williams et al, 2006;Christiansen et al, 2010).…”

“…Short-term behavioural changes can include changes in vocalisation, changes in movement to avoid vessels (most often observed as increased dive durations, increased swimming speeds and/or increased frequency in changes of the travel direction) (Marley et al, 2017) and changes to behavioural activity (changes in the percentage of the time spent feeding, resting, or socialising) (Christiansen et al, 2010;Meissner et al, 2015;Clarkson et al, 2020). Changes in behavioural activity are most likely to incur energetic costs to animals which experience cumulative disturbances from non-targeted boat traffic (Clarkson et al, 2020) or are targeted by tourism (Williams et al, 2006;Christiansen et al, 2010). Changes in movement to avoid vessels can increase energy expenditure in marine mammals (Williams et al, 2006;Christiansen et al, 2014) and/or decrease foraging activities and thus, decrease food/energy intake (Christiansen et al, 2013;Wisniewska et al, 2016).…”